The present invention relates to a rolling bearing assembly having a lubricating function, for example, a function of lubricating a main shaft or spindle of a machine tool with grease.
As a method of lubricating a spindle of the machine tool, a grease lubricating system that can be used maintenance-free; an air/oil lubricating system, in which a lubricant oil is mixed with a transport air so that the oil can be jetted into the interior of a bearing assembly through a nozzle; a jet lubricating system, in which a lubricant oil is jetted directly into the interior of a bearing assembly; and others have been well known. The machine tools in a state of the art are currently getting sped up in order to increase the machining efficiency and, to cope with this tendency, the air/oil lubricating system that can be sped up relatively inexpensively and easily is increasingly employed in most cases. However, since the air/oil lubricating system requires the use of air and oil supply devices as ancillary facilities and a large amount of air is also required, it has some problems associated with cost, noise, energy saving and resource saving. Also, an additional problem is found in that scattering of the oil leads to environmental contamination. In order to alleviate those problems, speeding up with the grease lubricating system has now come to attract attention of those skilled in the art and the demands therefor are indeed increasing.
Considering that the grease lubricating system is such as to accomplish the lubrication a bearing assembly only with a quantity of grease filled in the bearing assembly during the assemblage of the latter, it is generally considered that if the bearing assembly employing the grease lubricating system is operated at a high speed, degradation of the grease and a loss of the oil film on the raceway surface, particularly inner race, tend to occur as a result of heat evolved in the bearing assembly, resulting in a premature seizure. Particularly, in a high speed operating region, in which the dn value exceeds 1,000,000 (bearing inner diameter (mm)×number of revolutions (rpm)), it is virtually difficult to warrant the lifetime of the grease.
As a means to prolong the grease lifetime, various suggestions have recently been made. One of those recent suggestions includes the use of a grease reservoir in a portion of the raceway surface of the outer race to enable the bearing assembly to be operated at high speed with the lifetime of the grease increased (such as disclosed in, for example, the Japanese Laid-open Patent Publications No. 11-108068). Another one of those recent suggestion includes the use of a grease supply device provided externally to the spindle for supplying a quantity of grease to the bearing assembly to lubricate the latter (such as disclosed in, for example, the Japanese Laid-open Patent Publications No. 2003-113998).
However, it has been found that none of the foregoing suggestions is satisfactory when the number of revolutions (i.e., >dn value of 1,500,000) comparable to that achieved with the air/oil lubricating system and the maintenance-free feature are taken into consideration.
In view of the foregoing, the technology disclosed in the Japanese Laid-open Patent Application No. 11-108068 has been evolved in such a way that a gap, which communicates a grease reservoir, provided in close proximity to a stationary raceway member (for example, an outer race), with the vicinity of the raceway surface of the stationary raceway member, is formed in an peripheral surface of the raceway surface of the stationary raceway member, so that a base oil of the grease within the grease reservoir can be moved through the gap to a portion adjacent the raceway member by means of the capillary action of a thickening agent.
The lubricating system, in which the base oil is moved by means of the capillary action of the thickening agent as discussed above has been found involving a problem in that the base oil does not flow unless the oil is consumed at a tip of the gap, that is, a region in the vicinity of the raceway surface and, therefore, the supply of the lubricant oil tends to be too late at an operating condition such as an abrupt acceleration, failing to achieve an stabilized operation.